Disinfection of water on-board passenger transportation vehicles is necessary to guarantee water quality. This may include disinfection of potable water that is delivered to beverage makers, water that is delivered to sinks for hand-washing, water that is delivered to toilets for flushing, or water that is otherwise routed on-board the vehicle for various forms of use or consumption. For example, water systems on aircraft are complicated systems that usually include a tank with plumbing conduits and a pressurization system to deliver water to the points of use.
The issue of water quality, and in particular, of potable water quality, on passenger transportation vehicles and equipment, such as aircraft, trains, boats and ships, and the like is a point of interest for regulatory authorities. Regulatory standards have been enacted that require carried water on-board passenger vehicles to be disinfected according to certain standards. Passenger airlines and other transportation companies must thus implement appropriate aircraft water disinfection protocols.
U.S. Pat. No. 4,871,452 to Kohler, et al., entitled “On-Board Water Supply,” discloses equipment for purifying waste water from galleys, sinks, and toilets of aircraft. Waste water from these areas discharges to a tank, after which it passes through a mechanical filter, a bed of active carbon, ozone and osmotic stages, and a disinfection stage involving addition of chlorine and irradiation with ultraviolet (“UV”) light. Thereafter, the water is made available to aircraft passengers for certain uses.
U.S. Pat. No. 6,143,185 to Tracy, et al. entitled “Treatment System for Aircraft Toilet Waster Water” discloses alternate systems for decontaminating waste water from aircraft toilets, sinks, and galleys. They too include a mechanical particulate filter, activated carbon, and a source of UV light. Alternatively, according to the Tracy patent, the waste water may be exposed to microwaves or treated with chlorine or iodine. A sensor may be used to measure “the level of clarity of the treated water as an indication of its purity” and restrict opening of a control valve until acceptable clarity levels are obtained.
However, these systems and methods are primarily directed at purifying wastewater removed from the aircraft. Airlines and other passenger transport vehicle companies must also ensure that the potable water (i.e., drinkable water) aboard the aircraft is fit for human consumption by employing appropriate disinfection protocols. Disinfection upon upload and periodic disinfection sampling does not always adequately address the issue of contamination introduced in uploaded water, which is of particular concern for aircraft flying to and from, and being serviced in, non-industrialized areas. In addition, air must be introduced into the water storage and dispensing system on the aircraft in order to maintain pressurization, as well as to drain the system during routine servicing. This air can introduce pathogens that can multiply and cause unsanitary conditions and unacceptable water quality in the intervals between samplings or disinfection procedures. In effect, because the water storage and dispensing system is routinely exposed to the outside environment, potable water quality cannot always be ensured without some form of additional treatment. There is thus a need to further disinfect the water once it has been circulating in the aircraft water pipe system for a period of time, as the water may also need to be treated on an on-going basis, particularly as it is being delivered to the point of use.
Continuous treatment of potable water supplies presents its own set of potential problems to be solved, including continuous or semi-continuous dosing of the water with the requisite dosing equipment (metering and monitoring equipment, dosing agent storage equipment, and/or equipment for in-situ generation of the dosing agent). Accordingly, attempts have been made to purify water while on-board an aircraft or other passenger vehicles directly at the point of use. For example, U.S. Pat. No. 8,568,585 to Nolan entitled “Water Distribution System With Dual Use Water Treatment Unit” discloses systems for treating water by irradiation with UV lamp, along with an activated carbon or sediment filter.
Ultraviolet treatment eliminates bacteria, viruses, spores, and mold in the water and works similar to the way that strong sunlight can permanently purify water by making biological impurities inactive. Ultraviolet lamps are generally designed to destroy the links in these micro-organisms' DNA so that they are de-activated and cannot reproduce. The crucial hydrogen bonds that link the DNA chain together rupture when exposed to light between the wavelengths of about 220 nm to about 310 nm.
There are a number of water treatment solutions being employed and/or studied for use on-board aircraft. For example, one way that water can be treated is via UV mercury lamps. These lamps deliver an ultraviolet light to the water in the system and have been found beneficial because the treatment does not change the taste or odor of the water, it kills bacteria, viruses and protozoan, it is compact and easy to use, and it can prevent biofilm if the system is kept clean. However, one of the disadvantages of mercury UV lamps for water treatment is that they require a medium to high electrical demand, which means that when used on-board a vehicle such as an aircraft, they pull electrical power from the aircraft engines and/or an auxiliary power unit (APU). Increased usage of aircraft power from the engines results in higher fuel consumption and costs. Other disadvantages are that UV mercury lamps require cleaning and new lamps annually, and if a mercury lamp is broken, there exists a chance for mercury contamination of the water to be treated. Additionally, UV lamps take a while to power on if not in constant use. For UV lamps, the highest peak is generally mono-chromatic, in that the lamps generally only emit one effective wavelength, which is usually 254 nm for water treatment.
A further method of water treatment that has been explored is the use of ultraviolet light emitting diode (UV LED) light for water treatment. In addition to the mercury lamp benefits, the use of UV LED light also has the advantage of being able to use a wider UV band with multiple LED wavelengths, and it can offer a high power output with less power consumption than UV lamps. UV LEDs have greater longevity, power up quickly without requiring a delay time built into the system for the UV light source to reach its optimum UV energy output, and do not contain mercury. Some companies have been manufacturing UV lamps and LED systems for water sanitation and disinfection, but none of the available systems are designed for use on-board a transportation vehicle or an aircraft.
Therefore, a current need exists for a UV LED system for use in a vehicle or aircraft environment that is space efficient, energy efficient, accessible, and that is located in close proximity to a power supply and a water-system plumbing. It is also desirable to provide a system that can be added to existing systems, as opposed to having to replace the entire plumbing system on the vehicle.